Credits: overview: legislation
Social Security (Benefit) Married Women and Widows Special Provisions Regulations 1974 (SI 1974 no 2010) Reg 3 cover special provisions for starter credits for married women and widows. See NIM41210.
Social Security Credits Regulations 1975 (SI 1975/556) set out the rules for crediting contributors with earnings from 6 April 1975. See NIM41200.
Section 23A, Social Security Contributions and Benefits Act 1992 set out rules for Parent and Carers see NIM41250
There is equivalent legislation for Northern Ireland.